The present invention relates to a linear DC motor applied to a small precision machine tool or the like.
Coreless linear DC rotors capable of simply achieving precision positioning and high speed drive are suitable for small precision machine tools. A typical linear direct current motor of this type is shown in FIG. 11. A pair of linearly extending flat plate-shaped yokes 31, 1, an arranged parallel to each other, the ends of each of the two yokes are connected by two side yokes 33 and 34. A permanent magnet 41 is attached to the outer yoke 31 so that magnetic field is formed between the center yoke 1 and the outer yoke 31. The yokes 1, 31, 33 and 34 form a closed flux path. An excitation coil 5 wound on a suitable frame is mounted on the center yoke 1. The thrust (F) generated by the linear direct current motor is proportional to the product of magnetic flux density (B) of the magnetic field, the current (I) supplied to the coil, the length (L) of the coil in the magnetic field, and the number of turns (n) of the coil. The coil 5 is movable in the longitudinal direction of the center yoke 1, as shown by the double-headed arrow, by means of the thrust (F).
The advantage of such a linear direct current motor is its use of a small mover having low inertial mass. Also, as long as the magnetic field is uniformly formed, there is no cogging or torque ripple. This arrangement may be used to achieve a high precision servo control having excellent responsiveness.
An object of the present invention is to provide a linear direct current motor that efficiently cools beat generated in the coil.
A linear direct current motor according to the present invention comprises a center yoke extending in the longitudinal direction, an outer yoke arranged parallel to the center yoke, a permanent magnet for generating magnetic field between the outer yoke and the center yoke, and a coil assembly that is movable in the longitudinal direction and having an opening tough which the center yoke passes.
This coil assembly preferably includes a flat cooling pipe having a cross section elongated in the longitudinal direction and a U-shaped fold for passing the center yoke through, a manifold connected to the ends of the cooling pipe having a cooling medium inlet and a cooling medium outlet, and a coil wound around the cooling pipe and the manifold.
The cooling pipe preferably has a plurality of minute holes through which coolant can flow, the holes being aligned in the longitudinal direction.
Additional objects and novel features of the invention will be set forth in the description that follows or will be apparent to the artisan upon practice of the invention.